Amorphous thermoplastic resins are characterized by the fact that they can be molded by heating to a temperature above the glass transition temperature, thereby reducing their viscosity. It is greatly due to their good moldability that these amorphous thermoplastic resins have gained more and wider usages as compared to thermosetting resins.
In recent years, however, the market demanded better moldability of thermoplastic resins, and the improvement of their moldability has been an important problem in the art.
In particular, ABS resin, polycarbonates, polyarylates polysulfones, polyether sulfones, etc. have come into widespread use as a material replacing metal because of their high strength and heat resistance, and as engineering plastics, their uses have been extended to machine component parts, automobile parts, electrical and electronic component parts, etc.
These engineering plastics have high strength and heat resistance, but due to their high melting temperatures and melt viscosities, they frequently require high molding temperatures and pressures in a molding process. Hence, there has been a strong demand for the improvement of their moldability.
General-purpose plastics are also required to have good flowability because articles of a large size, a small thickness or a complex shape as demanded.
When amorphous resins are heated above their glass transition temperature, such an abrupt decrease of viscosity as in crystalline resins does not occur, and their molding is frequently difficult as compared with the crystalline resins.
Methods for decreasing the intermolecular cohesive force of polymers have been generally used to improve the moldability of such amorphous thermoplastic resins. For example, the following techniques have been used.
(1) To reduce the polarity of a polymer, it is modified by, for example, copolymerizing a monomer having low polarity.
(2) The internal plasticization of a polymer is accelerated by providing branches in the polymer.
(3) The degree of polymerization of a polymer is reduced.
(4) A highly flowable polymer such as ethylene/vinylacetate copolymer (EVA) or low molecular weight polyethylene is added.
(5) A plasticizer is added.
These techniques have various problems still to be solved, and they constitute great technical problems in the art. For example, according to the techniques (1) and (2), the modification such as copolymerization frequently results in a deterioration in the inherent properties (such as heat resistance) of the resin to be modified. According to the techniques (3) and (4), the mechanical strength of the polymer is reduced in many cases. In the technique (5), the heat resistance of the polymer is sacrificed.
The present inventors extensively investigated additives which can improve moldability of amorphous thermoplastic resins while inhibiting a reduction in mechanical strength or heat resistance, and now have come to believe that such additives desirably have the following properties.
(1) They have good compatibility with the matrix component during molding in a flowable system, and produce the same flowability improving effect as plasticizers.
(2) During use, namely in a condition in which the flowing of a system is suspended (at temperatures below the Tg or crystallization temperature of the matrix), they separate from a phase of the matrix component to prevent reduction of the heat resistance of the matrix.
To prevent the reduction of mechanical strength, such additives should have an interfacial adhesion strength higher than a certain point with respect to the matrix despite their separation from the matrix phase, and thus have an affinity for the matrix.
The present inventors have continued their investigations in order to define more specifically compounds satisfying the requirements (1) and (2), and judged that compounds meeting the following requirements (a), (b) and (c) are suitable.
(a) Low molecular weight compounds which have a unit compatible with a matrix component so as to act as a plasticizer during molding in a flowing system.
(b) Compounds which separate from the matrix phase by crystallization at temperatures below the molding temperature (temperatures below the Tg or crystallizing temperature of the matrix).
(c) Compounds which have relatively strong polarity so that they securely crystallize at temperatures below the molding temperature, and which contains a unit having an affinity for the matrix component so as to retain an interfacial adhesion strength with respect to the matrix even when they have separated from the matrix phase upon crystallization.
Extensive investigations based on this analysis led to the discovery that specific diamide compounds are effective on polyphenylene ether resin. An invention based on this discovery was applied for patent (Japanese Patent Application No. 233289/82).
The present inventors have continued their investigations and have found that the addition of the above-described diamide compounds to various thermoplastic resins produces similar results to those obtained previously with regard to the polyphenylene ether resin. This discovery has led to the present invention.